its when a person makes a mistake and though he attempts to make ammends and correct the mistake, he does it in the hardest way possible. The term originates from a character in the lord of the rings. In the prequel to Lotr, the Silmarillion, Glorfindel is an elf who dies in battle and goes to the elvish equivalant to valhala. But magically in Lotr a charachter by the same name returns and assists frodo. Tolkien later adimited it was a mistake. In stead of going back and changing the name of the charachter in the Silmarillion (which would have been easy since it was yet to be published at the time of tolkiens revelation) he made up this convaluted story about the valor calling Glorfindel back into service from the halls of mandos to fight against sauron, this all ends in glorfindel being reincarnated. So basically when you take the hard road to fixing a mistake.
Dude, why are you glorfindeling this situation. Just tell the bitch your sorry you cheated on her. You dont have to go and castrate your self, its totally unnessacary!